Ink-saturated endless ribbons are widely used as unicolor or multicolor ink ribbons for wire dot printers of computers, word processors or like devices. Such endless ribbons are manufactured by producing a plain-woven fabric using nylon or polyester multifilament yarn as warp and as weft, cutting said plain-woven fabric to a predetermined width so that the direction of warp coincides with the longitudinal direction of the ribbon, and joining both ends with each other to make the ribbons endless.
Those seamless ribbons are also known which are manufactured by producing a tubular, jointless (namely seamless) plain-woven fabric by double or tubular weaving and then fuse-cutting the same in the radial direction. In this case, contrary to the above-mentioned case of obtaining endless ribbons from plain-woven fabrics, the direction of weft of the fabric becomes the longitudinal direction (circumferential direction) of the ribbon. Seamless ribbons are advantageous just because, unlike endless ribbons, they have no junction. The present invention is concerned with ribbons of this kind, namely seamless ribbons.
In manufacturing such seamless ribbons, nylon or polyester multifilament yarn is generally used as warp and weft.
When 40d/34f multifilament yarn is used for weaving, the mean yarn density is selected as shown below in Table 1, for instance. Typical of those shown are quasi-high density products with a warp density of 146 yarns/inch, a weft density of 148 yarns/inch and a total density of 294 yarns/inch.
TABLE 1 ______________________________________ Warp density A Weft density B A + B (yarns/inch) (yarns/inch) (yarns/inch) ______________________________________ Ordinary density 132 142 274 product Quasi-high density 146 148 294 product High density 180 150 330 product Very high density 180 162 342 product ______________________________________
As regards the ribbon width, unicolor ribbons are relatively narrow and, as the number of colors increases, the width is increased accordingly. The circumferential ribbon length may be selected arbitrarily, although the upper limit to the ink ribbon circumferential length is by itself defined when the ribbons are intended to be loaded into standardized cassettes.
When the ink ribbon contained in a cassette, while making a round, arrives at the head, it is struck by the printer needle and the ink in the remaining part diffuses to resume homogeneity. When compact cassettes are used, ink ribbons are accommodated as folded in a zigzag fashion.
In impact printing, a platen, paper, a perforated mask, a ink ribbon and a head are arranged in that order, a dot printer needle protruding from the head is thrust against the ink ribbon to thereby strike the ink ribbon, through holes of the mask, against the paper, the shock being absorbed by the platen.
For information, Japanese Patent Publication H01-26349 (Kokai Tokkyo Koho S57-93187) discloses a method of manufacturing ink ribbon base cloths which comprises reducing, by 2 to 10%, the thickness, after scouring and setting, of a high density woven fabric composed of 20 to 120 denier synthetic fiber multifilament yarns as warp and weft and having a warp density of 150 to 220 yarns/inch and a weft density of 100 to 140 yarns/inch by pressing under heating, without rendering the same film-like, to render the same apparently reed mark-free. The thickness reduction is effected by conducting the pressing under heating using a heating and pressing means comprising two or more rolls and driving at least two rolls of the heating and pressing means at different speeds at a ratio in number of revolutions within the range of 1:1.1 to 1:2.0.
Seamless ink ribbons are not only used in Japan but also exported to and used in various other countries. In some countries, however, the paper on which printing is to be made, for example the paper produced in China, sometimes has a rough surface. (An investigation on the quality of paper produced in China revealed that the surface roughness is high both lengthwise and breadthwise, the ash content is high, and the content of kaolin type substances other than talc is high, thus making the surface hard). In Japan as well, the consumption of such rough-surfaced paper as regenerated or recycled paper is increasing from the viewpoint of resources saving.
When rough-surfaced paper is used, the ink ribbon accommodated in a cassette, running for printing, comes into contact with the paper and is rubbed by it so that the wear of the ink ribbon is more significant as compared with the case of standard printing paper. In other words, the rough paper plays the role of sandpaper, causing the wear of the ink ribbon. Therefore, when such rough-surfaced paper as the paper produced in China is used, the printable number of characters (i.e. the number of impressions) per ink ribbon is markedly reduced as compared with the case of quality paper, even when the ink ribbon itself still contains a considerable amount of ink.
Accordingly, it is an object of the present invention to provide a seamless ink ribbon showing a long life in printing even with rough-surfaced paper such as the paper produced in China as well as a method of manufacturing the same.
It is to be added that the reason why an attempt is made to eliminate reed marks from the high density woven fabric in the invention disclosed in Japanese Patent Publication H01-26349 as referred to above is that while a plurality of warps are drawn into each reed wire in manufacturing a flat woven fabric according to a conventional method of weaving, the so-called reed marks, namely interyarn gaps, are produced, when the warp density is high, in the warp direction (when in the ribbon form, in the longitudinal direction) at those portions of the woven fabric which correspond to the reed wires. Thus, the invention in said publication is based on the premise that it is concerned with a process for manufacturing ribbon base cloths by obtaining a flat woven fabric, cutting the same to a predetermined width with the warp direction being taken as the longitudinal direction of ribbons, and joining both ends together to give endless ribbons. When the warp density is increased, the occurrence of reed marks becomes unnegligible and it becomes a problem to eliminate them. Therefore, according to the invention in said publication, the thickness is reduced by 2 to 10% as compared with the original thickness to attain apparent absence of reed marks by means of two rolls driven at different circumferential speeds. The extent of thickness reduction is said to have a limit since when the thickness reduction exceeds 10%, the appearance becomes flat and film-like and the ink absorptivity becomes poor.
On the contrary, the present invention is concerned with a seamless ribbon. In contrast with the case where endless ribbons are obtained from a flat woven fabric, as mentioned above referring to the publication cited above, the weft direction becomes the longitudinal direction of the ribbon (circumferential direction) in the present invention, so that it is no more necessary to join both ends together and there is no reed mark problem, either. In other words, in the case of endless ribbons, warps run in the circumferential direction just like a railroad track and therefore, when there is a lack of uniformity (reed mark) in the track width, even blows of a dot printer can hardly make the track width uniform. In the case of seamless ribbons, the warps in the process of weaving are disposed, with a short length, in the direction of ribbon width, just like railroad ties and, even when ties are disposed at more or less irregular intervals, there is little influence on the quality of printing in the initial stage of use when the quantity of ink is abundant and, in addition, the first one or two blows of a dot printer automatically correct the irregularity in tie intervals. Thus, the decrease in ink quantity will not cause any substantial irregularities in the quality of printing.